Can this ram be mixed with apple's pre-installed ram? i've read that crucial memory has not played well with apple ram in the past.

Hey David!Thank you for reaching out to us, this is a great question. We obviously can't speak for Crucial or their product, however with only a single exception which comes to mind (16GB modules for the 2010-2012 Mac Pro) we have never had issues mixing Apple RAM with OWC RAM in the last 5-10 years. You would be just fine mixing this RAM with others, though we always advocate that the larger modules go in the "first" slots (ordered from top to bottom) as the machine may not "see" the larger modules if done the other way around. Let us know if you have another question, and if you want to get in to a longer form discussion I'd recommend getting in touch with our excellent support team at: https://www.owcdigital.com/support/contactHave a wonderful rest of your day!

If I add 2x16gb sticks to the 2x4gb sticks. Does it matter which slots I had them to? Let's say 1 is the bottom slot and 4 is the top?

The answer OWC gave was true in my case. My iMac came with Apple's two 4GB sticks located in slots 2 and 4. Initially I followed advice from another source to switch the location of those sticks to slots 1 and 3, and put the two 8GB OWC sticks in slots 2 and 4, purportedly because Apple had installed their sticks in the locations that are used first by the CPU, so it would be speedier to have the larger 8 GB there. I did that, and the machine did nothing for over a minute. After reading the answer by OWC here, I put the 8GB sticks in slots 1 and 2, and the 4GB sticks in slots 3 and 4, and the machine booted in a few seconds.

ASIN	B071K8K8LZ
Are Batteries Included	No
Best Sellers Rank	#107,530 in Computers & Accessories ( See Top 100 in Computers & Accessories ) #1,202 in Memory
Brand	OWC
Colour	Multi-coloured
Computer Memory Type	DDR4 SDRAM
Customer Reviews	4.3 4.3 out of 5 stars (121)
Date First Available	5 September 2017
Form Factor	SO-DIMM
Generic Name	RAM
Importer	CDM Digital Distributions Pvt. Ltd., First Floor, 32-A, Flat No. B-2 Gali No. 5, Molarband Extn. Badarpur South Delhi, Delhi 110044, 8744090999
Item Dimensions LxWxH	18 x 12.5 x 1 Centimeters
Item Height	1 Centimeters
Item Weight	23 g
Item Width	12.5 Centimeters
Item model number	OWC2400DDR4S16G
Manufacturer	OWC
Memory Technology	DDR4
Packer	CDM Digital Distributions Pvt. Ltd., First Floor, 32-A, Flat No. B-2 Gali No. 5, Molarband Extn. Badarpur South Delhi, Delhi 110044, 8744090999
Product Dimensions	18 x 12.5 x 1 cm; 23 g
RAM Size	16 GB
Voltage	1.2 Volts

OWC 16GB 2400MHZ DDR4 SO-DIMM PC4-19200 Memory Upgrade for 2017 iMac 27 inch with Retina 5K Display

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